The statements in this section merely provide background information related to this disclosure and may not constitute prior art.
Electrodeposition coating (“electrocoat”) compositions and methods are widely used in industry today. Electrocoat baths usually comprise an aqueous dispersion or emulsion including a principal film-forming epoxy resin (“polymer” and “resin” are used interchangeably in this disclosure), having ionic stabilization in water or a mixture of water and organic cosolvent. In automotive or industrial applications for which durable electrocoat films are desired, the electrocoat compositions are formulated to be curable (thermosetting) compositions. This is usually accomplished by emulsifying with the principal film-forming resin a crosslinking agent that can react with functional groups on the principal resin under appropriate conditions, such as with the application of heat, and so cure the coating. During electrodeposition, coating material containing the ionically-charged resin having a relatively low molecular weight is deposited onto a conductive substrate by submerging the substrate in the electrocoat bath and then applying an electrical potential between the substrate and a pole of opposite charge, for example, a stainless steel electrode. The charged coating material migrates to and deposits on the conductive substrate. The coated substrate is then heated to cure or crosslink the coating.
In a cathodic electrocoating process, the article to be coated is the cathode. Water-dispersible resins used in the cathodic electrodeposition coating process have amine functional group such as primary, secondary, tertiary, and/or quaternary amine moiety as a positively chargeable hydrophilic group. Such resins are presently made by batch processes that include a number of steps, which may require cooling before some steps. Continuous processes for manufacturing vinyl polymers are disclosed in Campbell et al., U.S. Pat. No. 6,552,144, Villalobos et al., U.S. Pat. No. 6,605,681, and the documents described in the background sections of these patents. These processes concern free radical, chain reaction polymerizations, however, and do not concern step-wise polymerizations such as those by which amine-functional epoxy resins are prepared.